Digital circuitry having a low power consumption can be provided by employing complementary pairs of transistors. Such a complementary pair of transistors is illustrated in FIG. 1. A p-type metal oxide silicon (PMOS) transistor 10 has a source coupled to first a voltage rail having a voltage VDD and a drain coupled to an output node 20. An n-type metal oxide silicon (NMOS) transistor 30 has a source coupled to the output node 20 and a drain coupled to a second a voltage rail having a voltage VSS, where VSS is less than VDD. A gate of each of the first and second transistors 10, 30 is coupled to an input node 40. The complementary pair of transistors can have either of two states, depending on an input voltage applied to the input node 40. When the input voltage is close to VDD, the PMOS transistor 10 is in a non-conducting state and the NMOS transistor 30 is in a conducting state. Consequently, the voltage between the source and drain of the NMOS transistor is small, and the output node 20 is at substantially the voltage VSS. Current cannot flow through either the PMOS or NMOS transistor 10, 30 because the PMOS transistor is in the non-conducting state. Conversely, when the input voltage is close to VSS, the NMOS transistor 30 is in a non-conducting state and the PMOS transistor 10 is in a conducting state. Consequently, the voltage between the source and drain of the PMOS transistor is small, and the output node 20 is at substantially the voltage VDD. Likewise, current cannot flow through either the PMOS or NMOS transistor 10, 30 because the NMOS transistor is in the non-conducting state. Therefore, the complementary pair of transistors operates as an inverter, converting a relatively low input voltage to a relatively high output voltage, and a relatively high input voltage to a relatively low output voltage, and has a very low power consumption. Low power consumption is of particular importance in relation to battery powered devices, especially for devices that are required to operate at a high frequency, such a wireless communication devices.
There is a requirement for improved low power circuitry.